Apparatus and process for carbon removal from fly ash

ABSTRACT

A new apparatus and process for efficient removal of carbon from fly ash has been developed, whereby carbon removal occurs through oxidation as combustion. The ignition of the carbon is accomplished by bulk heating and molecular impingement of a suspended layer of fly ash by a heated oxidizing gas strewn, and the desired level of carbon burnout is accomplished by maintenance of combustion conditions.

BACKGROUND OF THE INVENTION

Coal-fired power plants and other industrial facilities produce largeamounts of coal ash, commonly known as fly ash. Fly ash is a wasteproduct of the coal burning process, and must be disposed of properlydue to environmental regulations. The large amounts of fly ash producedyearly in the United States, therefore, pose a significant disposalburden for industry.

Although fly ash may be characterized as a waste product by someindustrial facilities, a beneficial use of fly ash as an additive forconcrete has been well established, provided the fly ash does notcontain excessive amounts of residual carbon left over from the coalburning process. Large volumes of low carbon fly ash may be used as apozzolonic material in concrete mixtures, both as a partial Portlandcement replacement and as a mineral additive. The use of fly ashincreases the quality of the product by adding strength, increasingsulfate resistance, and enabling more economical concrete production.However, the use of fly ash containing excessive amounts of carbon isunacceptable.

Many coal-fired power plants produce fly ash with low amounts ofresidual carbon, referred to as Loss-On-Ignition or LOI. However,numerous power plants and other facilities produce fly ash with LOIlevels above that which should be used in concrete. This high LOI flyash can be converted to a saleable product, if the amount of residualcarbon is reduced to or below acceptable carbon levels. Typically, LOIlevels of about 3% or below are acceptable for fly ash to be used as aconcrete additive.

Numerous processes for the removal of carbon have been proposed oremployed. For example, carbon reduction in fly ash by electrostaticseparation has been described in an article by David R. Whitlock,entitled "Electrostatic Separation of Unburned Carbon From Fly Ash" ofInternational Separation Systems, Inc., incorporated by referenceherein. The article proposes employing an electrostatic processinvolving contact charging separators. This is one of the two basicelectrostatic processes for dry particle separation. A more conventionalelectrostatic process involves a rotating drum corona-type separator,but it is impractical for carbon reduction in fly ash.

Another means to separate carbon from fly ash by flotation with tall oiland kerosene has been attempted. However, this method has not proveneconomical due to the large capital equipment and operating expensesincurred in such processing. Mechanical screening and air classificationmethods have also met with only limited success. Relatively largeamounts of fly ash is not suitable for processing according to thesemethods due to the methods' limitations on the size and weightdistribution of fly ash that can be processed.

Another method is described in U.S. Pat. No. 5,390,611 to Richard E.John, which is incorporated by reference herein, where the fly ash isradiatively heated using electrical means in a rectangular channel andpulled through the channel by feed screws. A small volume of air andadditional oxygen is fed into the channel through the feed screws to aidin ignition of the carbon in the fly ash. This method has met with onlylimited success due to low volumes of useable fly ash that is produced.

Other work has centered on the use of fluidized bed combustor means toremove carbon from fly ash. In the paper "Beneficiation of Fly Ash byCarbon Burnout" by J. S. Cochran and T. J. Boyd, incorporated byreference herein. This method suffers from high sensitivity to thevariability in ashes from different sources, owing to significantdifferences in fluidization and mixing characteristics, auto-ignitiontemperatures, reaction times, and propensity to form sinteredagglomerates. In addition, this approach advises the use of large andsophisticated air/handling and distribution systems that also employ gasparticulate separators. The operation and control of the processinvolves precision and allows for little variability in the individualoperating parameters without significant effect on others.

Similarly, U.S. Pat. No. 5,160,539 to Cochran, incorporated by referenceherein, reveals a method and apparatus for burning carbon from fineparticles of fly ash in a dry, bubbling fluid bed of previouslyintroduced fly ash particles. The method also has a propensity forcausing sintering and agglomeration of the fly ash, which is undesirablein fly ash to be used in concrete.

U.S. Patent No. 4,663,507 to Trerice, incorporated by reference herein,discusses a method and apparatus for reducing and measuring carboncontent in fly ash that employs microwave energy to induce combustion ofthe carbon. U.S. Pat. No. 4,705,409 to Trerice, incorporated byreference herein, is a division of U.S. Pat. No. 4,663,507.

German Patent No. 2,611,213 to Steag AG, incorporated by referenceherein, discusses making high quality clinker bricks from fly ash andclay, where the fly ash is initially roasted in the presence of a fuelsuch as coal dust or fuel gas. An external fuel source is used for theburnout operation.

Soviet Patent No. 734,162, incorporated by reference herein, discusses aprocess for thermally treating fly ash to reduce its carbon contentwhich uses a solid heat carrier such as quartz sand and createsaggregates of fly ash, rather than fine particles.

Japanese Patent No. 57,179,067 to Kobe Steel KK, involves sintering offly ash granules to form a lightweight aggregate, rather than fineparticles. Japanese Patent No. 57,100,972 to Kobe Steel KK, alsodiscusses a method for sintering fly ash granules.

The technology discussed in the above references leaves unsatisfied aneed by industry for an apparatus and method for reducing carbon in flyash that is simpler and more affordable to build and operate. Such anapparatus would, for example, eliminate the need for sophisticatedcontrol equipment and eliminate use of costly gas/particulateseparators. An apparatus is also needed that solves the problem ofsintering of the fly ash to form agglomerates without adverselyaffecting other physical properties of the fly ash for use in concrete.Further, an apparatus is needed that sufficiently meets the volumeoutput requirements of the concrete industry for fly ash use as apozzolonic admixture.

SUMMARY OF THE INVENTION

The present invention is directed to a new method and apparatus forremoving carbon from fly ash. The method comprises the steps oftransporting a bed of fly ash through an ignition chamber; contactingthe fly ash in the ignition chamber with an oxygen-containing gas at atemperature that is at least the ignition temperature of carbon for atime sufficient to ignite the carbon and the fly ash; transporting thebed of fly ash and ignited carbon to a burnout chamber; maintainingcarbon combustion in the burnout chamber at combustion-sustaining gastemperature and oxygen levels for a time sufficient to reduce the carboncontent of the fly ash to a desired level; and recovering the fly ashfrom the burnout chamber.

The apparatus of the present invention is directed to a vessel having anignition chamber and a burnout chamber; at least one support for a bedof fly ash moveably positioned within the vessel and constructed toallow passage of an oxygen-containing gas stream to contact the bed offly ash; means for moving the support containing a bed of fly ashthrough the ignition chamber and the burnout chamber; and a conduit influid communication between the ignition chamber and the burnout chamberfor transporting oxygen-containing gas from the ignition chamber to theburnout chamber to contact the beds of fly ash in each chamber. Analternative embodiment of the invention involves attaching the fly ashsupport directly to an ignition conveyor that travels through theignition chamber and burnout chamber.

The present invention results in an efficient, economical system forremoving carbon from fly ash. Among its many advantages, other thanthose mentioned elsewhere herein, is the use of two processing chambersinstead of one, as utilized by prior systems. This allows, after carbonignition, the majority of carbon burnout to occur in a separateenvironment that involves relatively lower levels of temperature andoxygen in the oxidizing gas stream for continued carbon burnout. Thistakes advantage of the self-sustaining carbon combustion properties ofthe carbon in the fly ash to accomplish economical processing. Anotheradvantage of the present invention is the reduction or elimination ofsintering problems.

Still other objects, features, and advantages of the present inventionwill be apparent from the following description of the preferredembodiments, given for the purpose of disclosure, and taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a preferred embodiment of the apparatus showinga vessel with an ignition chamber and a burnout chamber and multiple flyash layers suspended in racks that are passed through the ignitionchamber at the same time.

FIG. 2 is a partial schematic of a preferred embodiment of the supportsemployed in the practice of this invention showing suspension of a flyash layer in channels in the oxidizing gas stream.

FIG. 3 is a schematic diagram of an alternative preferred embodiment ofthe invention, wherein the fly ash is suspended in channels connected toa conveyor that may move continuously or intermittently through theignition chamber.

FIG. 4 is a schematic of an alternative preferred embodiment of theinvention, wherein the fly ash is suspended in channels connected to aconveyor that travels at one or more angles through the ignitionsection.

FIG. 5 is a schematic of an alternative preferred embodiment of theinvention, wherein the fly ash is suspended in channels connected to aconveyor that travels through the ignition section in multiplesubstantially horizontal passes.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

The present invention is directed to a new apparatus 1 for reducingcarbon in fly ash. A preferred embodiment of the present invention isshown in FIG. 1, where a carbon removal vessel compresses an ignitionchamber and a burnout chamber. Fly ash 6 is held in supports 2 to allowcarbon ignition to occur in the ignition chamber 7. The ignition chamber7 is preferably rectangular around its horizontal circumference, but maybe of any shape that is large enough to accommodate the supports 2. Oneor more supports 2 may be used. The supports 2 are preferably connectedin a grouping arrangement or rack 22. In this embodiment, the supports 2are preferably held together at each end with a rod or other device thatruns the length of the ends, substantially parallel to each other. Therods may be attached to side or bottom of the supports or in any otherinnumerable methods. The design of the support connectors is within thescope of those of ordinary skill in the art. The rack 22 is transportedthrough the ignition chamber 7, and following ignition, from theignition chamber 7 to the burnout chamber 10 by the ignition conveyor19. The gas passage gaps 3 are preferably accomplished by the spacing ofthe supports 2 on the rack 22. The individual supports 2 on each rack 22are preferably placed to allow the gaps 3 in one rack 22 to occurdirectly below the centerline of the individual support 2 of the nextrack 22 above it, while in the ignition chamber 7. This arrangementresults in an advantageous gas flow arrangement for impingement, as thegaps between the supports 2 of every other rack 22 are offset.

The supports 2 are loaded at the beginning of the process preferably byloader 8. Loading may be accomplished by any means suitable for thedelivery and distribution of fly ash in the supports 2 that is gradualenough to avoid excessive fall-through or escape of the fly ash from thesupports 2 during loading and is preferably a hopper. One preferredembodiment of the invention includes a collector 20 placed directlybeneath the supports 2 during ash loading that will collect fallen ashand provide part of a means 21 for returning any ash that has fallen orescaped from the supports 2 during loading.

Following support 2 loading with fly ash, the racks 22 are transportedinto the ignition chamber 7 by a conveyor 19 or other movement device.The conveyor 19 may be of any type commonly known in the industry thatis capable of transporting the racks 22 in a controlled, relativelyvibration and shock-free manner while maintaining a substantiallyconstant vertical orientation. The design of such a conveyor 19 is wellwithin the scope of those of ordinary skill in the art.

At the ignition chamber 7, the racks 22 join other racks 22 in avertical stack arrangement that preferably maintains a particularvertical spacing 25 between the racks 22. The number of racks 22 presentat any given time in the ignition chamber 7 may be varied and islimited, among other things, by the space available in the chamber andthe maximum allowable pressure drop through the successive racks 22 asdictated by the choice and limitations of the gas handling anddistribution system. In other words, the oxidizing gas stream preferablyis able to move through all the racks at a rate and temperature thatsustains ignition. Another variable in determining the number of racks22 to place in the chamber 7 is the amount of space desired between theracks 22. Preferably one to ten racks are used, but the most preferredembodiment utilizes four.

Means 28 for raking or physically disturbing the upper portions of thefly ash layers may also be employed preferably after at least low levelignition has occurred. This raking means 28 may be any fixed or moveabletype of device that is capable of imparting a physical disturbance tothe upper fly ash layer. The raking means 28 is a bar with downwardpointing pins in the preferred embodiment. The disturbance of the upperlayer of fly ash (preferably about the top half of the ash) after lowlevel ignition has occurred helps to retard any sintering of the extremeupper ash layer and facilitates carbon dioxide removal from the ashlayer that is created during carbon combustion.

Timing of the movement of the racks 22 into and out of ignition chamber7 is a function of the desired production rate and oxidizing gastemperature (which affects ignition time). Time in the ignition chamberis preferably in the range of about 1.0 to about 6.0 minutes. In thepreferred embodiment, the four racks 22 in the ignition chamber 7 arestationary in one position for approximately one-fourth of the total gasimpingement exposure time, whereafter they simultaneously move downwardand come to rest in the next lower position, maintaining the sameapproximate spacing 25 throughout. Alternative embodiments utilizecontinuous movement of the racks 22, while maintaining desired spacing25. After the lowest rack 22 reaches the last position in the chamber 7,it is transported by conveyor 19 out of the ignition chamber 7 and intothe burnout chamber 10 where it is unloaded.

In the preferred embodiment of the invention, unloading of the ignitedfly ash from the supports 2 is accomplished by a means 23 formechanically vibrating the rack 22, with assistance from the force ofthe gas from the burnout chamber gas distributor 15. These forces negatethe fly ash bridging effect over the open areas of the supports 2 andfacilitate fall-through of the ash from the supports 2 down to thesurface of a burnout receptor 11. Other commonly available means 23 maybe employed as well, such as mechanically dumping, pushing or otherwiseforcing the ash out of the supports 2. The burnout receptor 11 may be atray, a box, a conveyor or any number of things that will collect thefly ash. Preferably the receptor 11 is a conveyor.

The gas stream 5 is accelerated into the ignition chamber 7 by a gasmoving device 9 such as a fan, regenerative blower, or compressorassembly 9 and into the ignition chamber 7 where it may be heated by aheater 12. Alternatively, the gas may be heated first, either directlyor indirectly, before it passes into the ignition chamber 7. Gas heatingmay be accomplished by any means commonly known to the industry, and mayinclude direct or indirect heating means. The heated gas stream 5 isdirected substantially vertically in the ignition chamber 7 and impingeson successive racks 22 of fly ash layers in the suspension channels 2.Additional draft induction through means such as fans 13 may be employedto aid in maintenance of gas flow and dynamic pressure of the gas as itimpinges and passes each rack 22 of supports 2 and to aid in venting ofthe gas through exhaust 14, the burnout chamber gas distributor 15, anddistribution of the gas through gas recycle loop 16. From the recycleloop 16, the gas is reintroduced to the ignition chamber 7 for reuse asoxidizing impingement gas 5. Means such as a damper 17 may be used tocontrol the volume of recycled gas through the gas recycle loop 16.Another damper 17 may be used to control the intake volume of gas intothe ignition chamber 7.

After passing through distributor 15, gas is introduced to the burnoutchamber 10 where, among other things, it assists with the unloading ofthe ignited fly ash from the supports 2. Once the ignited fly ash isunloaded from the supports 2 onto the burnout receptor 11, carbonburnout continues due to exposure to the hot gas. A means 26 forsupplemental heating of this gas may also be used to maintain anecessary or desired gas temperature and to supply additional make-upgas. This supplemental heating means 26 may be of any means commonlyknown in the industry, but is a common self-contained direct-firedburner in the preferred embodiment and may be attached anywhere in theburnout chamber 10. The burnout chamber gas may be exhausted from theburnout chamber 10 by any device commonly known in the industry, but isan exhaust port 24 in the preferred embodiment. A draft induction fan 27also may be employed to aid in efficient gas distribution and dischargefrom the burnout chamber 10.

If the burnout receptor used is a conveyor, the travel rate of theburnout conveyor 11 may be adjusted to provide the desired residencetime of the fly ash in the burnout chamber 10 to accomplish a preferredlevel of carbon removal. Also, in coordination with the temperaturelevel of the gas in the burnout chamber 10, the travel rate of theburnout conveyor 11 may need to be decreased or increased as thetemperature of the gas increases or decreases, respectively. In thepreferred embodiment, assuming about 7% carbon in the incoming fly ashstream, the fly ash from the racks 22 will spend from about 6 to about 9minutes in the burnout chamber 10 for continued carbon combustion.Carbon combustion may be continued until essentially all the carbon isremoved. Preferably, combustion is continued until the fly ash containsabout 3% carbon by weight.

Means 30 for raking or stirring the ignited fly ash in the burnoutchamber 10 is provided to enable maximization of exposure of the ignitedcarbon particles to the oxidizing gas. This means 30 may be any devicecommonly known in the industry that will separate, rake or stir the ash,and in the preferred embodiment is a fixed grid with pins that protrudedownward vertically into the ignited layer of fly ash, enabling a rakingof the bed of fly ash to occur as the fly ash is transported on theburnout conveyor 11.

Referring to the drawings, FIG. 2 shows a partial schematic of apreferred embodiment of the supports 2 for the fly ash layer 6 in theoxidizing gas stream 5, and the gas passage gaps 3 utilized for gasrestriction and flow-by. The supports 2 may be constructed of any porousand/or gas permeable type of material that is capable of withstanding ahigh temperature oxidizing environment, while still providing adequatestructural support for the ash layer 6. In addition, the supports 2 arepreferably constructed with sufficient gas permeability to enable amaximum fly ash gas impingement area, and is also preferably constructedto avoid escape of the fly ash, particularly during transport.

Numerous materials and devices commonly known in the industry may beemployed for the supports 2, but the most preferred embodiment utilizesa #10 wire mesh made with about a 0.025 inch diameter wire, providingabout a 56.3% direct open area for gas impingement. Direct open area isthe surface area of the support that is open, such that gas may passthrough it unimpeded to contact the bed of fly ash. This design enablesthe fly ash 6 to be held in suspension after loading, yet maintains ahigh (56.3%) direct open area for oxidizing gas impingement.

Combinations of different numbers of wires per square inch (mesh) anddifferent wire diameters yield a range of specific net open areas. Thewidth of each individual opening in the mesh may be selected to maximizenet percentage direct open area, while minimizing the width of eachindividual opening. The net percentage direct open area can range from1-99%. A preferred range of direct open area is 40%-80%, and a morepreferred selection is 56.3%. The range of widths for each individualopening is preferably from approximately 0.0008 inches to approximately0.2 inches and in the preferred selection is 0.075 inches. A combinationof more than one mesh in sequence may also be used.

Furthermore, in an alternative embodiment of the invention, a rack 22 iscomprised of channels 2 without the above described gas passage gaps 3.In this embodiment, gas passage through the rack 22 is achieved byleaving certain supports 2 empty. Preferably, every other support 2 isleft empty. In addition, in yet another alternative embodiment of theinvention, each rack 22 is comprised of one flat sheet of mesh or othersuitable material. Fly ash 6 is then spaced intermittently on the rack22 to allow appropriate gas flow through the rack 22.

The supports 2 may be made of any material commonly known to be suitablefor use in high temperature oxidizing environments, and is stainlesssteel in the most preferred embodiment. Other suitable support 2materials would include perforated metal (preferably stainless steel),perforated ceramic materials, expanded metal, punched, slotted, drilledor grooved metal, and a variety of refractory materials. When wire meshis used, it is preferably fashioned in channels 2, as shown in FIG. 2,which permits intermittent gas passage gaps 3. The gas passage gaps 3enable, among other things, the oxidizing gas 5 bypassing the fly ash 6and the gas 5 impinging on the fly ash 6 to maintain continuous flow andeffective heat transfer. The width of the gas passage gaps 3 is tailoredto maintain a preferred amount of gas stream restriction which optimizesthe gas flow rate to stabilize the dynamic pressure of the oxidizing gasstream 5 impingement on the fly ash to prevent lifting the fly ash. Inone preferred embodiment, the width of the gaps 3 is about 0.5 inches.Numerous types of supports 2 may be used, including other designs madeof wire mesh, as discussed above.

In one preferred embodiment, nineteen supports 2 are connected in asubstantially parallel fashion along their lengths, with a structuralsupport such as a rod running along the ends of the channels 2 at eachend as described above. The channels 2 are approximately 3 inches wide,about 1 inch in height, and about 5.54 feet long. The rack created bythe connection of the nineteen channels 2 has the dimensions ofapproximately 5.54 feet by 5.54 feet. The ends of the channels 2 arepreferably closed.

In theory, any width or height or length of channels 2 may be used. Suchparameters are typically chosen to accommodate the processing of achosen volume of fly ash. The preferred embodiment discussed aboveinvolves the processing of about 5 tons per hour of incoming high carbonfly ash.

Rollers or other moving devices may be attached to the structuralsupports of the racks 22 to allow the racks 22 to be moved along C-railsor other devices for movement on the conveyor 19.

An even, properly directed gas stream 5 is preferably employed thatimpinges directly on the fly ash layer 6. Control of the direction,uniformity, and dynamic pressure of the gas stream may be aided byproper spacing and orientation of the gas passage gaps 3. The oxidizinggas stream 5 may be one of many compositions commonly known in theindustry that is oxygen-bearing, with one preferred embodiment of theinvention utilizing common air. In another preferred embodiment, theoxygen-bearing gas is comprised primarily of O₂ and inert gases. In yetanother preferred embodiment, pure O₂ is used. Air containingsupplemental oxygen enrichment may also be used. In the ignitionchamber, the gas stream preferably has about 5% to about 100% O₂ byvolume. In the burnout chamber, the gas composition by volume may rangefrom about 1% to about 100%. The oxidizing gas stream 5 is heated to atemperature level at or above that required to ignite and combust carbonwith oxygen. This ignition temperature level is a function of the amountof available oxygen as a concentration percent, and is at a minimumapproximately 750° F. to 800° F. at atmospheric pressure, if common airis used. Other temperatures may be used, provided they are above thatrequired to support carbon combustion with the gas stream chosen. Theselected temperature level will affect the time required to achievecarbon ignition and the level of carbon ignition saturation in the flyash layer. In the preferred embodiment of the invention, air is used andheated to a range of from about 1300° F. to about 1800° F., and mostpreferably to approximately 1700° F.

Low level carbon ignition is achieved in about a 1-inch ash layer height4 after approximately 2 minutes, with good ignition saturation occurringafter an additional approximately 75 seconds of continued gasimpingement. The support 2, as described above, is preferablyconstructed of #10, 0.025 inch wire mesh channels that are about 3inches wide, with gas passage gaps 3 of about 0.5 inches, but can be ofother combinations based upon the desired temperature, gas composition,and flow rate of the oxidizing gas and the desired ash layer height 4.The flow rate of the oxidizing gas in the preferred embodiment using airis 70 standard cubic feet/minute per square feet of ash impingement areaat 1700° F. The proper selection of these parameters is well within theskill of the ordinary engineer, and can be adjusted to suit the desiredproduction output goals. This may be easily done by adjusting theimpinging gas flow rate to a maximum value that avoids ash lofting andcarryover into the gas stream, after selecting the ash layer height 4and the spacing and orientation of the gas passage gaps 3 to meetdesired fly ash processing rates.

After achieving carbon ignition, exposure of the fly ash layers to theoxidizing gas stream may be continued to complete carbon burnout.However, preferably the fly ash containing the ignited carbon is notexposed to the same level of oxidizing gas stream for continued carbonburnout, but is allowed to burn or smolder at a reduced combustion ratethereby taking advantage of its self-sustaining carbon combustionproperties for economy purposes. This is accomplished by either reducingthe flow rate and/or the temperature of the oxidizing gas stream orutilizing exposure to a recovered and/or recycled gas stream. Thepreferred embodiment of the invention, as described above, utilizes asecond chamber 10 that maintains conditions sufficient for continuedcarbon combustion of the ignited fly ash. The second chamber 10 does notutilize direct gas impingement on the fly ash suspended in a gas stream.Rather, a recovered/recycled gas stream is preferably introduced to thechamber 10. Further, fly ash exposure to this oxygen-bearing gas may beenhanced by a means 30 that rakes or stirs the ash. The ignited carbonusually continues to burn at a rate proportional to the temperature andoxygen exposure.

Means 18 for cooling the fly ash 6 may be any that are commonly known inthe industry, which are well known to those skilled in the art. In thepreferred embodiment, the means 18 is a solids cooler such as a bulkflow heat exchanger.

Once the desired carbon burnout has occurred, the fly ash 6 isdischarged from the burnout chamber 10, preferably by the burnoutconveyor 11, or if no conveyor 11 is used, then the ash may bedischarged. Any commonly available means for discharging fly ash fromthe burnout receptor 11 such as vibration, air-assisted, or mechanicalmay be employed in all embodiments, and are well within the scope of theordinary engineer. The discharged fly ash may then be air cooled orforce cooled.

An alternative embodiment of the invention, as shown in FIG. 3,comprises the same arrangement as the preferred embodiment of FIG. 1,except that the supports 2 are connected directly to the ignitionconveyor 19 with the heated oxidizing gas stream 5 making a single passthrough the suspended fly ash layers 6 before they are dumped onto theburnout receptor 11 after ignition. The ignition conveyor 19 returns thesupports 2 to the loader 8 for reloading with fly ash. The conveyor 19may operate with continuous or intermittent motion. In addition, thisarrangement may utilize a fixed means 28 for upper ash layer raking thatis fixed or moveable. Either a fixed or moveable means 28 for raking ordisturbing the upper ash layer may be used in any embodiment of theinvention.

FIG. 4 is another preferred alternative embodiment of the invention, andcomprises an apparatus similar to the embodiment of FIG. 3, except thatthe supports 2 are connected directly to a conveyor 19 that travels atone or more angles through the ignition chamber 7 while maintaining thesubstantially horizontal orientation of the supports 2, thereby enablingmultiple passes of the oxidizing gas on fly ash layers to occur. Theconveyor angle chosen may be varied from 0° to 90°, but in the preferredembodiment is 45 degrees. The number of angled turns in the ignitionchamber 7 may be varied, depending on the chosen size of the chamber andthe desired residence time of the supports 2 in the chamber 7. Inaddition, the alternative embodiment shown in FIG. 4 illustrates a means32 for allowing a portion of the hot oxidizing gas stream 5 to flow pastthe ignition chamber 7 and contact the supports 2 in the burnout chamber10. This means 32 also helps maintain the ignition and combustion of theignited carbon in the fly ash during travel to the burnout chamber 10.The gas conducted by means 32 into the burnout chamber 10 may assistwith unloading of the supports and the maintenance of continued carbonburnout in the burnout chamber 10. Assistance with support 2 unloadingoccurs when gas flow is directed onto the ash 6 in the supports 2 and isforceful enough to cause fly ash fall-through and carryover.

FIG. 5 is another preferred alternative embodiment of the invention, andcomprises an arrangement similar to the embodiment of FIG. 3, exceptthat the supports 2 are connected directly to a conveyor means 19 thatmakes multiple substantially horizontal passes through the ignitionchamber 7 while maintaining a substantially horizontal orientation ofthe supports 2. This enables multiple impingements of the oxidizing gason the beds of fly ash to occur. The length and number of horizontalpasses in the ignition chamber 7 can be chosen based on the desiredchamber size and operating efficiency.

Still yet another alternative embodiment of the invention is one wherethe supports 2 maintain a substantially vertical orientation on theconveyor 19 in the ignition chamber 7, thereby allowing multiple passesof the oxidizing gas stream 5 to occur for economy purposes.

Additionally, an alternative embodiment of the invention may utilize therecycling and reuse of a portion of the gas exhausted from the burnoutchamber 10 for ignition chamber 7 use. Control of the volume of burnoutchamber 10 gas that is recycled can be achieved by any commonlyavailable means known in the industry, and is a damper 17 in thepreferred embodiment.

The preferred method of this invention is a new process for reducingcarbon in fly ash. In the preferred embodiment, fly ash with a highcarbon content is put into a loader 8 which feeds the fly ash intosupports 2 which are part of racks 22. In one preferred embodiment, thewidth of the loader 8 is coincident with the length of the support 2.Alternatively, a smaller loader 8 may travel back and forth along thelength of each supports 2 to provide a relatively even, approximately 1inch layer of fly ash in each support 2. Preferably, a collector 20below the loader 8 collects fallen fly ash and recycles it via means 21to the loader 8. As discussed above, the loader is preferably a hopper,but loading may be accomplished by any means suitable for the deliveryand distribution of fly ash in such a manner as to be gradual enough notto facilitate excessive fall-through or escape of the fly ash from thesupport 2 during loading. The means 21 may be a conveyor or other devicefor moving solids. Such devices are well known to those skilled in theart. Once a rack 22 of supports 2 has been filled with fly ash, ittravels along ignition conveyor 19 to the ignition chamber 7. Theconveyor 19 may be of any type commonly known in the industry that iscapable of transporting the racks 22 in a controlled, relativelyvibration and shock-free manner while maintaining a constant relativelyhorizontal orientation. The design of such a conveyor means 19 is withinthe scope of knowledge of one skilled in the art. In the preferredembodiment, four positions are available in the ignition chamber 7 forthe racks 22. A rack 22 first enters the ignition chamber 7 at a topposition in the chamber 7 and then moves consecutively down the chamberto three lower positions. The time that a rack 22 spends in the ignitionchamber 7, may be varied considerably, but in the preferred embodimentis about 3.5 minutes. The racks 22 spend about one-fourth of their timein the ignition chamber 7 at each of the four positions.

Oxygen bearing gas 5 travels through the ignition chamber 7 at atemperature and flow rate that will ignite the carbon with the oxygen.In the preferred embodiment, the gas stream 5 is accelerated by a gasmoving device 9 such as a fan or regenerative blower or compressorassembly into the ignition chamber 7 where it is heated directly byheaters 12. Alternatively, the gas may be heated first, either directlyor indirectly, before it passes into the ignition chamber 7. Gas heatingmay be accomplished by any means commonly known to the industry, asdiscussed above, and may include direct or indirect heating means. Theheated gas stream 5 is directly substantially vertically in the ignitionchamber 7 and impinges on successive suspended fly ash layers 6 in thesuspension racks 22. Additional draft induction means such as a fan 13may be employed to aid in maintenance of proper gas flow and dynamicpressure of the gas as it impinges and passes each rack 22 and to aid inventing of the gas through exhaust 14, through recycle loop 16 orthrough burnout chamber gas distributor 15.

In the ignition chamber 7, the racks 22 are spaced in the preferredembodiment in a vertical stack arrangement that maintains a particularvertical spacing 25. The number of racks 22 present at any given time inthe ignition chamber 7 may be varied and is limited by the spaceavailable in the chamber 7 and for the other reasons discussed above.Preferably, from 1 to 10 racks 22 are stacked in the ignition chamber 7,but in the most preferred embodiment, 4 are stacked.

Once the fly ash in a rack 22 has been subjected to at least low levelignition, it is raked or physically disturbed by raking means 28. Means28 disturbs approximately the top half of the fly ash layer. This rakingmeans 28 may be any fixed or movable type of device that is capable ofimparting a physical disturbance to the upper fly ash layer. In thepreferred embodiment, the means 28 is a bar with downward pointing pins.

After a rack 22 attains the last position in chamber 7, it istransported by conveyor means 19 out of the ignition chamber 5 and intothe burnout chamber 10 where it is unloaded. Unloading of the ignitedfly ash from the supports 2 is accomplished preferably by a means 23 formechanically vibrating the racks 22, with assistance from the force ofgas from the burnout chamber gas distributor 15. After passing throughdistributor 15, a portion of the gas 5 leaving the ignition chamber 7 isintroduced to the burnout chamber 10, where, in part, it assists withthe unloading of the ignited fly ash from the supports 2. These forcesnegate the fly ash bridging effect over any open areas of the supports 2and encourage fall-through of the ash from the supports 2 down to thesurface of the burnout receptor 11. As discussed above, other commonlyavailable means for unloading the supports 2 may be employed.

Once in the burnout chamber 10, the fly ash is continually exposed tohot gas 5 transported through the burnout chamber gas distributor 15.The continual exposure to the oxidizing gas stream 5 sustains carboncombustion within the burnout chamber 10. A majority of carbon burnoutoccurs in the burnout chamber 10 in an environment that preferablymaintains less than the temperature and oxygen levels used for carbonignition in the ignition chamber. Alternatively, a means 26 forsupplemental heating of the gas passed into the burnout chamber 10 bythe distributor 15 may be used to maintain a specific gas temperature orto supply additional make-up gas. In the preferred embodiment, assumingabout 7% carbon in the incoming fly ash stream, the fly ash from theracks 22 will spend from about 6 to about 9 minutes in the burnoutchamber 10 for continued carbon combustion. The travel rate of a burnoutconveyor 11, if one is used, may be adjusted to provide the desiredresidence time of the fly ash in the burnout chamber 10. Carboncombustion may be continued until essentially all the carbon is removed.Preferably, combustion is continued until the fly ash contains about 3%carbon by weight.

The burnout chamber gas is expelled from chamber 10 by any devicecommonly known in the industry, but is an exhaust port 24 in thepreferred embodiment. A draft induction fan 27 may also be employed toaid in efficient gas distribution and the discharge of the gas from theburnout chamber 10.

While in the burnout chamber 10, the fly ash on the burnout receptor orconveyor 11 is raked or stirred by means 30 to provide for greaterexposure of the carbon particles to the oxidizing gas. This means 30, asdiscussed above, may be any device commonly known in the industry thatwill separate, rake or stir the ash, and in the preferred embodiment isa fixed grid with pins that protrude downward vertically into theignited layer of fly ash, enabling a raking of the ash to occur as thefly ash is transported.

When the fly ash reaches the end of conveyor 11, it preferably is dumpedinto a solids cooling means 18 to allow cooling of the carbon reducedfly ash 6 prior to unloading. However, forced cooling of the fly ash isnot necessary in all embodiments of the invention, as discussed above.The cooled fly ash 6 may be off-loaded to a truck, storage silo, barrel,any other type of storage container, or a dump site.

Referring back to the oxidizing gas stream 5, which exits the ignitionchamber 7 through induction fan 13, the stream 5 may also be recycledthrough loop 16 for reuse in the ignition chamber 7. Dampers 17 may beplaced periodically through the gas distribution system to control thegas stream flow. The selection and placement of such equipment is wellwithin the skill of the ordinary engineer.

An alternative method of the invention, referring to FIG. 3, comprisesthe same method as discussed above, except that in the ignition chamber7 the supports 2 are connected directly to an ignition conveyor 19. Inthis method, the heated oxidizing gas stream 5 makes a single paththrough the suspended fly ash layers 6 before the fly ash 6 is dumpedonto the burnout receptor 11. The conveyor means 19 may operate withcontinuous or intermittent motion.

Another preferred alternative method of the invention, referring to FIG.4, comprises a method similar to the preferred embodiment describedabove (with respect to FIG. 1), except that the supports 2 are connecteddirectly to an ignition conveyor 19 that travels at one or more anglesthrough the ignition chamber 7 while maintaining substantiallyhorizontal orientation of the supports 2. The oxidizing gas thereforeimpinges upon the fly ash layers multiple times. As described above, thechoice of angles will affect how many passes the gas makes over eachlayer of the fly ash. Contemporaneously, the oxidizing gas stream 5 maybe channeled to the burnout chamber 10 behind a partition 32. Gasconducted by a partition 32 into the burnout chamber 10 may be used toassist with supports 2 unloading and the maintenance of continued carbonburnout in the burnout chamber 10, as discussed above.

An additional alternative preferred method, referring to FIG. 5,comprises a method similar to that described above with respect to FIG.2, except that the supports 2 are connected directly to conveyor 19 thatmakes multiple horizontal passes through the ignition chamber 7,allowing multiple impingements of the oxidizing gas on the fly ashlayers 6.

Some common engineering elements such as gauges, valves, controllers andthe like are not shown or described except when necessary for theunderstanding of the invention. For the most part, selection andplacement of such equipment is well within the skill of the ordinaryengineer. Although the above process and apparatus are described interms of the above preferred embodiments, those skilled in the art willrecognize that changes in the process and apparatus may be made withoutdeparting from the spirit of the invention. Such changes are intended tofall within the scope of the following claims:

What is claimed is:
 1. An apparatus for lowering the carbon content infly ash comprising:a vessel having an ignition chamber and a burnoutchamber; at least one support for a bed of fly ash moveably positionedwithin the vessel and constructed to allow passage of anoxygen-containing gas stream to contact the bed of fly ash; means formoving the one or more supports containing a bed of fly ash through theignition chamber and the burnout chamber; and a conduit in fluidcommunication between the ignition chamber and the burnout chamber fortransporting oxygen-containing gas from the ignition chamber and toburnout chamber to contact the beds of fly ash in each chamber.
 2. Theapparatus of claim 1, wherein the ignition chamber further comprisesconduits for gas inflow to and outflow from the ignition chamber.
 3. Theapparatus of claim 2, wherein the ignition chamber further incorporatesa gas moving device at the inflow conduit.
 4. The apparatus of claim 2,wherein an induction fan is incorporated into the outflow conduit forthe ignition chamber.
 5. The apparatus of claim 2, wherein a recycleloop for the gas stream is connected from the outflow to the inflowconduit of the ignition chamber.
 6. The apparatus of claim 2, whereinthe conduit in fluid communication between the burnout chamber and theignition chamber further incorporates a burnout chamber gas distributor.7. The apparatus of claim 2, wherein an exhaust is incorporated into theoutflow conduit for the ignition chamber.
 8. The apparatus of claim 1,wherein the burnout chamber further incorporates an exhaust port.
 9. Theapparatus of claim 8, wherein an induction fan is incorporated into theexhaust port.
 10. The apparatus of claim 1, wherein a gas heating deviceis incorporated into the ignition chamber, whereby the oxygen-containinggas may be heated.
 11. The apparatus of claim 1, wherein the supportsare connected to form a rack.
 12. The apparatus of claim 11, wherein thenumber of supports in a rack is nineteen.
 13. The apparatus of claim 11,wherein two or more racks are stacked in the ignition chamber.
 14. Theapparatus of claim 13, wherein the number of racks is four.
 15. Theapparatus of claim 1, wherein the ignition chamber further comprises ameans for raking the fly ash in the supports.
 16. The apparatus of claim1, wherein the burnout chamber further comprises a supplemental heaterfor the gas stream.
 17. The apparatus of claim 1, wherein the burnoutchamber further incorporates means for unloading the supports.
 18. Theapparatus of claim 1, wherein the burnout chamber further incorporates aburnout receptor that collects fly ash unloaded from the supports. 19.The apparatus of claim 18, wherein the burnout receptor is a conveyor.20. The apparatus of claim 18, wherein the burnout chamber furtherincorporates a means for raking the fly ash on the burnout receptor. 21.The apparatus of claim 1, wherein the means for moving the one or moresupports through the ignition chamber and burnout chamber is an ignitionconveyor.
 22. The apparatus of claim 1, wherein the vessel furthercomprises a means for cooling the processed fly ash.
 23. An apparatusfor lowering carbon content in fly ash comprising:a vessel having anignition chamber and a burnout chamber; at least one support for a bedof fly ash; an ignition conveyor that attaches directly to the supportsand travels through the ignition chamber and burnout chamber; and meansfor transporting oxygen-containing gas through the ignition and burnoutchambers.
 24. The apparatus of claim 23, wherein the ignition conveyormakes one substantially horizontal pass through the ignition chamber.25. The apparatus of claim 23, wherein the ignition conveyor travels attwo or more angled passes through the ignition chamber.
 26. Theapparatus of claim 23, wherein a partition diverts a portion ofoxygen-containing gas to the burnout chamber so that said gas contactsalready ignited carbon.
 27. The apparatus of claim 23, wherein theignition conveyor makes multiple substantially horizontal passes throughthe ignition chamber.
 28. An apparatus for lowering the carbon contentin fly ash comprising:a vessel having an ignition chamber and a burnoutchamber; at least one support for a bed of fly ash moveably positionedwithin said vessel and constructed so as, in an ignition position, toallow impingement of an oxygen-containing gas stream against said bed offly ash at a plurality of locations along the undersurface of said bed;means for impinging said gas stream upwardly against said bed of fly ashwhile avoiding lofting and carryover of the fly ash into the gas stream.29. The apparatus of claim 28 wherein said apparatus furthercomprises:means for moving said support between said ignition positionand one or more other positions within said vessel, said apparatus beingadapted to cause another contact of said gas stream with said bed of flyash when said bed is in at least one of said other positions.